The present application is based on and claims priority from Japanese Patent Applications 2000-242411, filed Aug. 10, 2000 and 2001-106342, filed Apr. 4, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an engine start-stop control system for an automotive vehicle.
2. Description of the Related Art
In order to protect environment and natural resource, it is recommended to stop the engine of an automotive vehicle while the vehicle is waiting for the traffic signal to change. For this purpose, an automatic engine start-stop control system has been developed. Such an automatic engine start-stop control system automatically stops the engine when a driver stops the vehicle with the engine running at an idle speed (hereinafter referred to as the idle stop operation) and automatically starts the engine when the driver operates an existing lever or pedal, such as an acceleration pedal, to start the vehicle. Therefore, it is necessary for the engine start-stop control system to stop and start an engine without delay in order to prevent traffic jam.
JP-B2-7-42909 discloses such an engine start-stop control system, in which current supplied to the solenoid of a magnet switch is gradually increased until the main contact thereof closes and is gradually reduced after the main contact has closed to start the engine. The above engine start-stop control system moderates the speed of the pinion of the starter engaging with the ring gear of the engine, so that the pinion and the ring gear can be prevented from being damaged.
However, since the pinion moves toward a ring gear of the engine at a low speed, it takes a considerable time for the pinion to engage the ring gear. If terminal voltage of a vehicle battery becomes lower than a normal level due to over-discharge thereof, the engagement speed may become so long that traffic jam is caused.
Therefore, a main object of the invention is to provide an improved engine start-stop control system that can stop and start engine without delay and without damage to the starter and the engine.
According to a main feature of the invention, an engine start-stop control system for an automotive vehicle includes
first means for supplying current to a solenoid of a magnet switch of a starter motor at 100% duty ratio until a first predetermined time passes; and second means for supplying current to the solenoid at a duty ratio that is less than 100% after the first predetermined period passes until a second predetermined period passes.
Therefore, the current supplied to the solenoid generates sufficient force to pull a plunger of the magnet switch, which brings the pinion near a ring gear of the engine in a short time. Then, the current is controlled to a low level just before the pinion engages the ring gear to reduce the pulling force of the plunger so that the impacting speed of the pinion can be reduced. As a result, impacting shock given to the pinion and the ring gear is moderated, and the lifetime thereof is increased.
The above system may have third means for supplying current to the solenoid at 100% duty ratio after the second predetermined period passes until a third predetermined period passes. As soon as the pinion is brought in contact with the ring gear, the pulling force of the solenoid is increased so that the pinion is further urged, via the plunger, to engage the ring gear completely. This shortens the time to start the engine and also eases the engagement stress at a limited portion, which may be damaged because of incomplete engagement due to insufficient urging force.
The above system may have fourth means for controlling at least one of the first, second and third predetermined periods according to voltage level of said battery or an amount of current supplied to the solenoid. Accordingly, even if the battery terminal voltage is comparatively low, the system can operate properly.